This invention relates to the decorative marking of surfaces, such as the surfaces of sheets of glass and other hard but abradable material. More particularly, the invention is concerned with the etching of such surfaces with abrasive particles, such as particles of aluminum oxide, silicone carbide, and silica sand (such etching often being referred to as "sandblasting"), especially with respect to decorating glass for picture frames, mirrors, and other decorative glass products.
While the invention is not limited to the decorative marking of glass, and in fact has broad application to the marking of surfaces generally, the present discussion will be limited to the etching of glass sheets used in the picture framing art. Also, the abrasive surface treatment commonly known as "sandblasting" will be referred to as "etching" herein.
It is known in the art, such as from U.S. Pat. No. 2,608,800, that decorative etching of glass may be accomplished by masking the surface of the glass except for the portion to be marked. This can be done with a stencil or a sheet of plastic contact film that is subsequently cut to expose the surface portion to be etched. Then, the exposed portion is treated with abrasive particles propelled such as in a high velocity stream of air against the glass. This technique of decorative etching is seldom employed in the picture framing trade, however, due to the necessity of using expensive and specialized sandblasting equipment and procedures. Unless the glass sheets are relatively small and can be etched in sandblasting cabinets, the operation must be performed in rooms specially equipped for this purpose. As such, it is an extremely dusty and hazardous operation, requiring special safety suits and protective masks. Accordingly, custom picture framing shops are not known to be equipped to perform sandblasting operations or decorative etching of the type described. The method and apparatus of the present invention, however, reduce the difficulties indicated above and afford other features and advantages heretofore not obtainable.